This invention relates to an underwater sand pump, and more particularly to the improvement of an agitator of the underwater sand pump.
One conventional underwater sand pump comprises an agitator mounted on an output shaft of a motor which, upon rotation, agitates sands in the water bed and whirls sand in an upward direction and a suction pump which sucks the whirled sand along with the whirled water. In such underwater sand pump, however, since the agitator and the suction opening of the suction pump are disposed so close to each other, the downward water stream caused by the agitator and the upward water flow caused by an impeller of the suction pump interfere with each other, thereby the sand excavating operation with such sand pump suffers an extremely poor efficiency.
For resolving the above defects of the above suction pump, an improved type of underwater pump was developed and such pump is disclosed in Japanese Utility Model publication No. 51-38005. The pump is substantially constructed such that a cylindrical perforated strainer with the lower end thereof closed with an end plate is provided between the suction opening and the agitator and a circular opening which has an inner diameter almost equal to the outer diameter of the agitator is formed in the end plate of the perforated strainer and an umbrella-shaped body which loosely engages with the circular opening is mounted on the output shaft of the motor.
Due to such construction, upon rotation of the output shaft of the motor, sand and water can be clearly separated into the agitating flow which moves downward to the sea bed and the suction flow which moves toward the pump by the umbrella-shaped body so that the interference between the agitating flow and the upward flow can be prevented.
However, since the agitator is disposed away from the umbrella-shaped body, a vacuum is often produced in the space between the agitator and the umbrella-shaped body resulting in cavitation. This cavitation causes the vibration of the drive shaft and produces bubbles around the agitators and furthermore, small stones which exist in the sand may hit the pump, thus causing damage to the pump. Therefore, such sand pump is also less than optimal in terms of the sand excavating efficiency as well as the maintenance thereof.
Accordingly, it is an object of the present invention to provide the underwater pump which can overcome all the above defects of conventional underwater pumps. Namely, the underwater pump according to this invention is completly free from cavitation during the sand excavating operation and thereby has an improved excavating efficiency.
The present invention, in summary, discloses an underwater pump comprising an underwater motor having an output shaft thereof extending downwardly on which an impeller is mounted, a pump casing encasing the output shaft, an agitator fixedly attached to the lower extension of the output shaft, the agitator consisting of a truncated cone and a plurality of vanes radially mounted on the circumferential wall of the truncated cone and a cylindrical perforated strainer disposed between a suction inlet of the impeller and the agitator, the strainer being provided with an end plate at the bottom end thereof in which a circular opening is formed, wherein the improvement is characterized in that flow separating means for separating an agitation flow and a suction flow is disposed in the circular opening, that the flow separating means is integrally and contiguously mounted on the upper end of the truncated cone of the agitator and that the flow separating means has an outer diameter substantially equal to an inner diameter of the circular opening of the end plate of the perforated strainer.